The bedload layer in a 1D sand-gravel morphodynamic model

Abstract

The effective thickness of the bedload layer over a river bed can be schematised as the total volume of bedload sediment that is in transport, divided by the surface. In practice, this layer is considered to have a constant thickness over time. Main question of this thesis is whether this assumption is valid. By analyzing the mass balance, it is possible to gain an approximation of the reality. By means of numerical approximations, it is possible to build a morphological model which imitates these equations. This imitation makes it possible to analyze the effect of specific parameters on the sediment transport and the bed surface elevation. In this way, the effect of neglecting the derivative over time of the effective thickness of the bedload layer can be investigated. The model of a river section of the Rhine between Emmerich am Rhein and Lobith results in a maximum influence of the derivative of the effective thickness of the bedload layer on the morphodynamic changes as the result of one flood event that is smaller than 4%. A parameter study makes it possible to test the obtained result on sensitivity. Because the morphodynamic model is based on a lot of input parameters, a well founded choice between the large variety of parameters has to be made. A rough sensitivity test shows that the at maximum 4% influence on the derivative is subject to a possible variation of approximately a factor 2, depending on the variation in the input parameters.Hydraulic EngineeringCivil Engineering and Geoscience